The Applicant proposes to study microsomal electron transport in liver, kidney, and lung with specific emphasis on the role of NADPH-cytochrome c (P-450) reductase in its interaction with the various cytochrome(s) P-450 and other physiological acceptors, such as cytochrome b5, in the various organs. A variety of experimental approaches are being used, including the study of microsomal fractions of liver, lung, and kidney with respect to substrate specificity; the purification of microsomal constituents from these organs and reconstitution of their activities; the determination of the microsomal lipid milieu for the various organs which maximizes the respective activities measured; the immuno-chemical localization, at the light and electron microscopic levels, of the various reductases in liver, lung, and kidney, and the study of the mechanism by which NADPH-cytochrome c (P-450) reductase reduces various electron acceptors, e.g., cytochrome(s) P-450 and b5.